Commercial flocks of poultry, such as chickens, turkeys, ducks, geese, quail and the like, can generally be classified as belonging to one of three flocks: the primary (or master) breeding flock, the secondary breeding flock, and the food flock. Poultry eggs can likewise be loosely classified into two general categories, hatching eggs, which are fertile eggs that are to be hatched into chicks (for the breeding flock or the food flock), and table eggs, which can be either fertile or infertile eggs that are intended for direct consumption.
The food flock, as its name implies, is intended for direct consumption, i.e., these are the birds that are purchased for food at a local grocery store. The secondary breeding flock produces both hatching eggs, from which the food flock is hatched, and table eggs intended for direct consumption. Birds are selected for membership in this flock based upon a number of factors, including the number and size of eggs produced and the characteristics of the birds hatched from these eggs (the food flock). The primary or master breeding flock also produces hatching eggs, from which the secondary breeding flock is hatched, but not table eggs. These birds are selected for membership in the master flock based upon their particular genetic characteristics as evidenced in the secondary breeding flock (second generation) and the food flock (third generation).
When food borne pathogens began to pose a major health issue, the poultry industry began to experience public pressure to remedy the problem of these pathogens. It has been found that a primary source of pathogen infection in chicks is the hatchery. Indeed, it is well documented that after a chick has been hatched, the chances are over 90% that it is a carrier of a number of pathogens which are dangerous to both consumers and other poultry in the flock (breeding or food). These pathogens include Salmonella spp. and Campylobacter spp., both of which have caused numerous cases of human intestinal diseases.
Even with the high probability of pathogen infection at hatching, the natural resistance to infection that develops in growing poultry nevertheless reduces the percentage of infected birds in the overall flock population. For example, in the case of salmonella, the percentage of contaminated chicks in the flock will drop from 90% of the population immediately following hatching to about 26% of the population in the houses in which the birds are grown and/or maintained. The effect of this bird's natural resistance is even more pronounced when the incidence of pathogen infection at hatching is reduced. For example, research has shown that chicks which are not infected with salmonella at hatching will resist infection during the period they are growing (e.g., 60 days or so) even if the grow house is contaminated.
The residual contaminated birds, however, remain a source of pathogen infection for the rest of the flock, breeding or food.
Moreover, in the case of the food flock, these residual contaminated birds are the most likely source of dangerous food borne pathogens when the flock is harvested.
A process known as competitive exclusion was proposed by Nurmi and Rantala, Nature, vol. 241, pp. 210-211 (1973), as a means for reducing the level of pathogen infection in poultry. This process involves administering intestinal bacteria from mature, healthy poultry to chicks whose intestinal bacteria were not yet established. The bacteria administered to the chicks competes with any pathogens that might be present in the gut of the chick, reducing the rate of colonization by the pathogens and thus the level of infection.
This method, however, has not provided completely satisfactory results. For example, the competing bacteria administered to the chicks may not colonize at a sufficient level to satisfactorily reduce the rate of colonization by the pathogen. In addition, over time, the pathogens tend to adapt to the presence of the competing bacteria and can actually colonize at a faster rate, thereby out-competing the competitive bacteria.
Thus, while the poultry industry has responded by treating many of the symptoms of the problems of pathogens, no practical solution has been offered which will cure the problem at its source: the hatchery. Accordingly, there remains a need for a system and method for controlling microorganisms associated with poultry.